1. Field of the Invention
The present invention relates generally to a photo film transporting device, and more particularly to a photo film transporting device applied to a camera using a photo film such as an APS film.
2. Description of Related Art
An advanced photo system (APS) camera using an APS film is widely known. The entire surface of the APS film is coated with a transparent magnetic recording layer for recording information. In addition, a cartridge of the APS film has a visual exposure index (VEI) indicating the state of the film. The VEI has a circular hole, a semicircular hole, an X-shaped hole and a rectangular hole formed in the bottom of the cartridge, and a white tongue that rotates with a spool is provided in the cartridge. The VEI stops the tongue at the circular hole, the semicircular hole, the X-shaped hole or the rectangular hole to show a white circle, semicircle, X or rectangle, respectively; and they indicate that the film has not been used, that it has been half exposed, that it has been completely exposed, and that it has been developed, respectively.
When the film is rewound into the cartridge after all the frames are exposed, the VEI needs to show the X indicating that the film has been exposed. The spool keeps rotating even after the film is completely rewound into the cartridge, and it needs to immediately stop when the white tongue comes to the X-shaped hole.
To control a motor for transporting the film, a photo film transporting device needs an electric current supply route from a power source to the motor, a loop that returns a regenerate current generated from the motor when the electric current supply route is cut in order to stop the motor, and so on. Also, the photo film transporting device needs a plurality of switching circuits that form and cut the electric current supply route and the loop, and circuits that turn on and off the switching circuits. This makes the photo film transporting device complicated and expensive.
In view of the foregoing, it is an object of the present invention to provide a simple and inexpensive photo film transporting device that drives and stops a motor for transporting a film.
To achieve the above-mentioned object, the present invention is directed to a photo film transporting device that drives a motor to transport a photo film, the photo film transporting device comprising: a first switching device that forms an electric current supply route for supplying an electric current from a power source to the motor when a voltage of a control terminal of the first switching device is a first voltage, the first switching device cutting the electric current supply route when the voltage of the control terminal of the first switching device is a second voltage; a second switching device that forms a loop for returning a regenerate current generated from the motor to the motor when the voltage of a control terminal of the second switching device is the second voltage, the second switching device cutting the loop when the voltage of the control terminal of the second switching device is the first voltage; and a voltage switching device that switches a voltage of a common terminal connected to the control terminals of the first switching device and the second switching device between the first voltage and the second voltage, wherein: the first switching device forms the electric current supply route and the second switching device cuts the loop to drive the motor when the voltage switching device sets the first voltage; and the first switching device cuts the electric current supply route and the second switching device forms the loop to stop the motor when the voltage switching device sets the second voltage.
The first switching device comprises a bipolar transistor, and the second switching device comprises a field-effect transistor.
The voltage switching device sets the first voltage when a high voltage is applied from a CR timer composed of a capacitor and a resistor to the voltage switching device; the voltage switching device sets the second voltage when a low voltage is applied from the CR timer to the voltage switching device; and an amount of driving time of the motor is controlled by stopping supplying electric charges to the capacitor.
The supply of the electric charges to the capacitor is started and stopped according to whether or not the film is at a predetermined position.
The voltage switching device comprises a field-effect transistor.
The photo film transporting device further comprises a contact connected to the common terminal, the voltage of the contact is switched between the first voltage and the second voltage according to a state of a Visual Exposure Index of a cartridge containing the film, wherein the voltage of the control terminals of the first and second switching devices is set to the first voltage when at least one of the contact and the voltage switching device sets the first voltage.
According to the photo film transporting device of the present invention, the voltage switching device switches the voltage of the common terminal connected to the control terminals of the first switching device and the second switching device between the first voltage (for example, the low voltage) and the second voltage (for example, the high voltage). When the voltage switching device sets the first voltage, the first switching device forms the electric current supply route and the second switching device cuts the loop, and this drives the motor. When the voltage switching device sets the second voltage, the first switching device cuts the electric current supply route and the second switching device forms the loop, and this stops the motor. Therefore, the motor can be driven and stopped with one voltage switching device, and this makes the circuit simple and less expensive.
If the second switching device is the FET, the control current for turning on the FET is not necessary, and this saves electricity.
If the voltage switching device is the FET, electricity can be saved. If the CR timer times the switching by the voltage switching device, the inexpensive element (for example, the ceramic capacitor) can be used, and this lowers the cost.
The contact that switches the voltage of the common terminal between the first voltage and the second voltage according to the state of the VEI is connected to the common terminal, and the voltage of the control terminals of the first and second switching devices is the first voltage when at least one of the contact and the voltage switching device sets the first voltage. Thus, the motor is driven when both of the contact and the voltage switching device do not set the second voltage. Therefore, when the voltage switching device sets the first voltage, the motor can be driven regardless of the state of the VEI; and when the voltage switching device sets the second voltage, the motor can be stopped according to the state of the VEI.